1. Field of the Invention
The present invention relates to a sheet-shaped heat-generating body, and more specifically, to a sheet-shaped heat-generating body that is flexible and free from displacement or one-sided distribution of the heat-generating substance.
2. Description of the Related Art
Recently, a heat-generating body has been widely used as a type of warming means, for instance, as a disposable and portable body warmer. Such a heat-generating body comprises a heat-generating substance mainly consisting of an oxidizable metal powder such as iron powder or aluminum powder which is received in an air-permeable bag, and which is capable of generating heat upon contact with the air.
Although such a heat-generating body is advantageous in that it can be easily used, it entails the following defects. When the heat-generating body is used, for instance, to warm a human body or food, the heat-generating substance tends to displace downward under gravitation not only during movement of the human body or during transportation of the food but even while the heat-generating body is motionless. This leads to deformation of the heat-generating body, which can be uncomfortable or inconvenient to the user. In addition, the heat-generating characteristic of the heat-generating body per se may change, deteriorating its heat-generating performance.
In order to eliminate these defects, various proposals have been made on structures where a heat-generating substance is supported by a sheet-shaped substrate so as to prevent displacement of the heat-generating substance.
Such proposals include a method of supporting a heat-generating substance by a net-shaped member of metal gauze, plastic or gauze (Japanese Patent Laid-Open No. 84246/1978), a method of superimposing an oxidizable metal in the form of foil or the like on a sheet-shaped oxidation assistant comprising fiber of activated carbon, etc. impregnated with a chloride and water (Japanese Patent Laid-Open No. 37181/1988), and a method of supporting a compressed heat generating agent on paper (Japanese Utility Model Laid-Open No. 42018/1989).
However, since a heat-generating substance tends to mass when mixed with water, etc., it is very difficult, from the viewpoint of fabrication, to directly support a heat-generating substance on a net-shaped member while assuring uniform distribution. With a structure where an oxidizable metal in the form of, e.g., foil is superimposed on a sheet-shaped oxidation assistant, since the oxidizable metal and the oxidation assistant are not uniformly integrated together, sufficient heat generating performance cannot be expected. Further, a structure where a heat-generating agent is merely compressed onto and supported by paper, involves a risk that the heat-generating substance may separate from the paper-during use.